There is a need for the rapid production of prototypes. The stereolithography method used in the production of prototypes, needs complicated support structures for the preparation of prototypes from a liquid (resin), and the resultant prototypes have relatively poor mechanical properties, attributable to a limited number of starting materials.
Another process for rapid prototyping is selective laser sintering (SLS), which has now become widespread. In this process, polymer powders in a chamber are selectively irradiated briefly with a laser beam, which results in the melting of the powder particles on which the laser beam falls. The molten particles coalesce and solidify again relatively rapidly to give a solid mass. Complex three-dimensional bodies can be produced simply and rapidly by this process, by repeatedly applying fresh layers of polymer and irradiating these layers.
The process of laser-sintering (rapid prototyping) to form moldings composed of pulverulent polymers is described in detail in U.S. Pat. No. 6,136,948 and WO 96/06881 (both DTM Corporation). The SLS processes described have the disadvantage of requiring expensive laser technology. The laser, functioning as energy source, is extremely expensive and sensitive, as also is the optical equipment needed for the production and control of the laser beam, such as lenses, expanders, and deflector mirrors.
Other processes have been developed for rapid prototyping, but have not been introduced into the market. For example, WO 01/38061 describes a process for producing prototypes which is based on the use of sinter inhibitors that inhibit sintering, initiated by the introduction of energy, of pulverulent substrate in selected regions. This process can operate without any complicated laser technology. However, the specific introduction of heat cannot be used with this process. Also, another disadvantage of this process is that the surrounding powder which was not melted still contains the inhibitor, and therefore, cannot be recycled. In addition, this process requires the development of new software, specifically because it is the surrounding area that is printed, and not, as in other cases, the cross section of the part. For undercuts and changes in cross section, large-surface-area application of inhibitors is needed. In addition, there is the risk of heat build up in the developing prototype.
In U.S. Pat. No. 5,338,611, the use of microwave radiation for the melting of polymers is described. In this process, pulverulent polymers and nano-scale carbon black are used. However, this reference does not describe the production of prototypes. Reference DE 197 27 677 describes a method of generating prototypes, by exposing selected regions of pulverulent layers to a focused microwave beam. The controlled microwave beam bonds the exposed pulverulent substrates within a layer, and also bonds these substrates to the pulverulent substrates in the layer situated thereunder. Bonding takes place via adhesive bonding, sintering, or fusion. This process also requires complicated technology in order to ensure that the microwave radiation reaches only the selected regions.
All of the prototype-production processes known use relatively complicated technologies. In particular, the use of lasers or focused microwave radiation requires high precision, and therefore, requires apparatus which is expensive and susceptible to failure. Although the known processes are suitable for producing prototypes, these processes are, however, unsuitable for rapid manufacturing applications, or for applications in the home.